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Thursday, April 17, 2008

About Ignalina nuclear power plant

Recently we had a discussion here regarding Ignalina nuclear power plant to be shut down by the EU in 2009, claiming that the reactor RBMK is not safe enough to meet with the European standards. However, it is not so widely known that during the last 8 years Western experts were examining this plant to check its security, and they haven’t found any reason for its closure. The decision to shut down Ignalina reactor looks more a political then security-reasoned one, playing on the bad image of RBMK reactors after Chernobyl.

Although the reactor RBMK-1500, running now at Ignalina, is far not the same as Chernobyl RBMK-1000 when it comes to security. Reactors of graphite type have significantly improved their security and adjusted the construction since the mid-80s. Second block of Ignalina, launched in August 1987, has much more developed system of accident localization comparing to RBMK-1000. The current heat power of RBMK-1500 on Ignalina plant is 4200MWt, maximum electrical power 1360MWt. This plant supplies electricity to more than 70% of Lithuanian consumers, and rest is exported. Operation term for reactor of this type is 45 years, the last RBMK reactor in Russia is planned to be shut down in 2035.

Here are some characteristics of Ignalina RBMK reactor, taken from the website of the plant, including the description of security and monitoring systems used.

The RBMK-1500 reactor is the largest power reactor in the world. The thermal power output of one unit is 4800 MW, the electrical power capacity is 1500 MW. The Ignalina nuclear power plant, like all the stations with RBMK reactors, has a direct cycle configuration - saturated steam formed in the reactor proper by passing the light water through the reactor core is fed to the turbine at a pressure of 6,5 MPa. The light water circulates over a closed circuit.

The first stage of the nuclear power project comprises two 750 MW turbines. Each generating unit is provided with a fuel handling system and unit control room. The turbine room, waste gas purification and water conditioning rooms are common for all the units. Ignalina NPP generates about 74% of electricity consumed in Lithuania.

TECHNICAL DATA ON RBMK-1500 REACTOR

Coolant

light water (steam/water mixture)

Heat cycle configuration

single-circuit

Reactor power, MW

thermal power output

4800

electric power capacity

1500

Core dimensions, mm

diameter

11800

height

7000

Square lattice pitch, m

0.25х0.25

Thickness of graphite reflector, mm

end

500

lateral (side)

880

Maximum graphite temperature, C°

750

Fuel

uranium dioxide

Initial enrichment, for U235, %

2.0

Rate of burned fuel MW·d/kg

21.6

Number of channels per lattice, pc:

fuel channels

1661

control rod channels

235

reflector cooling channels

156

Saturated steam pressure in separators, MPa

7.0

Feed water temperature, C°

190

Saturated steam flow rate, t/h

8800

Coolant flow rate through reactor, m3/h

40000 - 48000

Coolant temperature, C°

at fuel channel inlet

260

at fuel channel outlet

285

Mean mass steam content at outlet

0.291

REACTOR CONTROL AND PROTECTION SYSTEM

The control and protection system is intended for reliable follow-up of the reactor performance and its safe operation. The system provides start-up, automatic maintenance of power at the set level, allows control of energy distribution along the radius and heightwise of the core, compensates for fuel burn-up, provides protection of the reactor under emergency conditions.

The control and protection system is built of fail-safe and redundant devices using integrated circuits to receive and process signals from various sensors, as well as to present the reactor status information to the operator. The reactor power release and its distribution are controlled by 211 carbide boron rods placed in the control channels and moved by individual servomotors mounted on the top of the control channels. The control rods are cooled with water from a special loop.

Out of the total numbers of rods, 40 ones are used for energy distribution control through the height of the active zone of the reactor. 24 rods perform the function of prompt emergency safeguard introduced into the active zone within 2.5 seconds under definite emergency situations. The remaining rods are unified and serve the function of reactivity scramming, automatic maintenance of the reactor power release at the set level, control of energy distribution over the core radius.

REACTOR PROCESS MONITORING SYSTEM

The reactor process monitoring system provides the operating personnel with information and inputs data into the control and protection system.

The reactor process monitoring system consists of the following functional elements:

data logging system which provides follow-up, processing and presentation of the data;

self-contained energy release control system which provides measurement, control and indication of energy release in the reactor channels'

self-contained system monitoring tightness of fuel assembly cladding and providing measurement, control and indication of coolant activity rise:

system monitoring integrity of the fuel and control channels and providing measurement of temperature and indication of relative humidity of gas pumped through the gas paths of the core;

system monitoring coolant flow in the reactor channels;

system monitoring temperature of the main and auxiliary equipment of the reactor.

The data logging system is configured in a three-level hierarchy using computers SM-1M and SM-2M and interface facilities.

The energy release monitoring and control system includes energy release detectors providing inertialess measurement of neutron flux density along the radius and height of the core, and the equipment to process information and signals on the control board.

The system monitoring tightness of the fuel assembly claddings includes scintillation gamma-spectrometer sensors, equipment, to ensure operation and movement of sensors in the intertube space of the steam lines, and facilities for processing and output of data.

The system monitoring the coolant flow through the reactor channels consists of tachometric transducer, and equipment affording frequency-to-analog signal conversion.

The system monitoring the temperature of the reactor equipment contains mainly heat-resistant cable heat-electric transducers.

RADIATION SAFETY

The RBMK-1500 reactor is provided with special elements and systems ensuring radiation safety of the nuclear power plant and the environment both under normal operating conditions and in the emergency cases. The radiation safety and doze control systems include:

The system monitoring tightens of fuel rod cladding specially designed for the RBMK-1500 reactors and applying modern techniques for detection of faulty fuel rods and computer-based data logging provides the core radiation control. The computerized radiation doze control system at the nuclear power plants with reactors of the RBMK-1500 type is provided with facilities monitoring radiation exposure of all components and systems of the station.

All this helps to maintain the radiation conditions at a safe level by implementing the purposeful actions (removal of leaky fuel assemblies, decontamination, replacement and repair of the equipment. To reduce emissions of noble radioactive gases. A two-stage system is used for cleaning gaseous and aerosol effluents discharged through a 150 m high stack into hold-up chamber. When noble gases pass through it, their activity is reduced due to natural decay.

The second stage-activity suppression facility purifies and reduces activity of noble radioactive gases by the method of dynamic sorption using the radiochromatographis char columns. To reduce radioactive aerosol emissions at the nuclear power plants with the RBMK-1500 reactors provision is made for purification facilities absorbing aerosols by special filters. The nuclear power plants with the RBMK-1500 reactors use a closed-circuit water supply system. Liquid radioactive effluents undergo special treatment. Radioactive discharge into air and water is monitored continuously using instruments of the computerized radiation dose control system.

The external radiation exposure surveillance service at the nuclear power plant with the RBMK-1500 is equipped with instruments to analyze concentration of radionuclides in the elements of the environment. The health physics laboratory is provided with facilities and sampling methods, dozimetric, radiometric, spectrometric instruments for objective assessment of the radiation conditions in the environment.

I suppose this will pour some light on the claims that Ignalina has to be shut down just for the sake of not having another Chernobyl. According to Russian experts, for example, Alexandr Potapow (interview to Regnum, 11.04.2006) who are most familiar with this type of reactors, their modern characteristics completely exclude the possibility of a new Chernobyl, because these reactors correspond to the world standards of security.

There might be also an interest from the side of Western reactor constructors to work on replacement of Ignalina power plant reactor, because such a project was already discussed by governments of Lithuania, Latvia, Poland and Estonia. Although, as figures above and the discussions below show, this is far not a necessary step. If someone wants to earn on this – it’s another matter.

Some might suspect I am lobbying the Russians and their reactors. My own parents live 5 km from the plant, Braslaw region, Belarus. Basically on the other side of that lake in the photo.

6 comments:

Besides the improvements discussed in the past sicne Chernobyl (e.g., higher enriched fuel, more control rods inserted, etc.) did the the plant change the purity of their graphite? The Chernobyl graphite was less pure than even Fort St. Vrain which was a 70's design. Higher purity graphite eliminates much of the oxidation risk.

Robert, I will write to Ignalina and check this data about graphite purity with them as the most reliable source, since this information is not on their website and I did not find anything on the web so far.

From a technical point of view, there is no reason to worry that the Ignalina reactor will experience a Chernobyl like accident. That accident required a very specific set of circumstances.

It is also not hard to read between the lines spouted by the people who are adamant about shutting down the plant. They are very interested in supplying the replacement power, either in the form of the fossil fuels that will be burned starting as soon as the plant stops producing electricity or in the form of any replacement nuclear plant that will eventually be built.

In any case, there will be a tremendous exchange of resources and plenty of opportunity for profit.

If I were a Lithuanian, I would continue to encourage my government to resist the pressure to shut down the plant by continuing to ensure that accurate information about its design and operation is widely distributed.

Still no answer from plant engineers when it comes to graphite purity, they rather prefer to keep it as a secret or just do not want to reply to a message in Russian (some Lithuanians are like that - they know Russian but they principally refuse to speak it).

My guess is that they have not changed the graphite purity. It may be that the higher purity graphite is too expensive for the utility. The Japanese use extremely pure graphite in their HTTR plant, but it is a small (30 MWt) reactor and so requires less graphite.

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